The reactions between [(C5H5)(2)MCl2] (where M = Ti, Zr, Hf) and Li[B5H8] in a variety of solvents have been investigated. In the case of Zr, a pale orange solid, mu-(Cp2ClZr)B5H8 (1), is formed in 70% yield. Compound 1 exists as a B5H9 cage with a Cp2ClZr moiety replacing a bridging H atom. The variable temperature NMR spectra of 1 reveal two fluxional processes, one (DeltaG(double dagger) = 54 kJ mol(-1)) which renders a plane of symmetry in the molecule and a higher temperature one (DeltaG(double dagger) = 48 U mol-1) which renders all the basal B atoms equivalent. Dynamic processes are suggested to account for these observations. Passage of a CH2Cl2 solution of 1 through silica gel affords 2, [(CP2Zr)(2)B5H8][B11H14], a yellow, air-stable, crystalline solid, in 14% yield. The cation in 2, [(Cp2Zr)(2)B5H8](+), consists of a distorted spiro[2.2]pentane-like B-5 moiety comprising two B-3 triangles sharing a naked boron vertex. The two triangles are twisted 73degrees with respect to each other, and the two [Cp2Zr] groups bond in a trihapto arrangement to the two opposite B-B-B edges. Each exterior B-Zr edge is H-bridged, and the B atoms possess terminal hydrogens. Reactions of Cp2HfCl2 with Li[B5H8] lead to the formation of the analogue of 2, [(Cp2Hf)(2)B5H8][B11H14] (3). The precursor to 3, that is, the Hf analogue of 1, is not observed. Reaction between Li[B5H8] and Cp2TiCl2 afforded no identifiable products, but reaction with CpTiCl3 resulted in cage coupling and the formation of B10H14.